This invention relates to a method of preparing a noble metal-containing catalyst. More particularly, this invention relates to the addition of noble metals to a zeolite catalyst.
Shape selective catalysis utilizing molecular sieves was first demonstrated by P. B. Weisz and V. J. Frilette in J. Phys. Chem. 64, p. 302 (1960). Since then, the shape selective catalytic properties of various zeolites have been extensively demonstrated. For example, N. Y. Chen and W. E. Garwood in "Some Catalytic Properties of ZSM-5, a New Shape Selective Zeolite", Journal of Catalysis, 52, pp. 453-458 (1978) described the shape selectivity of ZSM-5.
The effect of the addition of noble metals on the properties of zeolite catalysts has been of substantial interest in the literature. P. B. Weisz, V. J. Frilette, R. W. Maatman and F. B. Mower in "Catalysis by Crystalline Aluminosilicates II. Molecular-Shape Reactions", Journal of Catalysis, 1, pp. 307-312 (1962) described a shape selective olefin hydrogenation catalyst comprising platinum incorporated in zeolite A. In U.S. Pat. No. 3,140,322 to V. J. Frilette and P. B. Weisz, a process is disclosed for hydrogenation using a platinum containing zeolite. In U.S. Pat. No. 3,226,339 of V. J. Frilette and R. W. Maatman, a process is described for the preparation of a platinum- or palladium-containing zeolite catalyst. U.S. Pat. No. 3,575,045 of J. N. Miale discloses the use of a platinum entrained zeolite A for selective hydrogenation.
A catalyst and process for selectively hydrogenating ethylene in the presence of propylene utilizing a zeolite in conjunction with a hydrogenation metal is disclosed in U.S. Pat. No. 3,496,246. N. Y. Chen and P. B. Weisz in "Molecular Engineering of Shape-Selective Catalysts", Kinetics and Catalysis, Chem. Eng. Prog. Symp. Serial No. 73, Vol. 63, 1967, p. 86, described a platinum catalyzed hydrogenation employing a phosphine-poisoned, platinum-exchanged sodium mordenite zeolite.
An excellent summary of the art of metal loaded zeolite catalysts and shape selective catalysis is given in Zeolite Chemistry and Catalysts, J. A. Rabo, ed., ACS Monograph 171 (1976). Of particular interest is Chapter 10, "Catalytic Properties of Metal-Containing Zeolites" by K. M. Minachev and Y. I. Isakov and Chapter 12, "Shape-Selective Catalysis" by S. M. Csicsery.
Catalysts such as ZSM-5 combined with a Group VIII metal are described in U.S. Pat. No. 3,856,872 to Morrison. It is disclosed in this patent that the catalysts be preferably incorporated in a porous matrix such as alumina. A Group VIII (hydrogenation) metal may then be added after incorporation with the zeolite in a matrix by such means as base exchange or impregnation. In one embodiment, the metal is added in the form of chloroplatinic acid.
U.S. Pat. No. 4,188,282 discloses particularly preferred forms of noble metal-containing zeolites such as ZSM-5 formed by the crystallization of the zeolite from a forming solution containing noble metal ions, such as those of platinum.
U.S. Pat. No. 4,209,384 teaches the preparation of a hydroprocessing catalyst comprising an alumina-mordenite carrier material and a platinum component. The catalyst is prepared by incorporating the platinum component with a solution having a pH greater than about 6.
There are also methods known in the prior art to decrease the amount of noble metal required to achieve a particular desired catalytic effect by increasing the degree of dispersion. For example, U.S. Pat. No. 4,568,656 teaches loading and uniformly distributing platinum onto a zeolite-L. The zeolite-L is contacted with an aqueous solution containing a platinum salt in a non-platinum metal salt, wherein the non-platinum metal salt is present in solution in an amount which is critical to preventing the formation of acid sites as well as avoiding an excess of metal ions in the form of a salt which could block the pores of the zeolite-L.
U.S. Pat. No. 4,615,997 teaches a method for preparing hydroisomerization zeolite catalysts containing a highly dispersed noble metal. The method includes mix mulling the zeolite, noble metal and binder into an extrudate and chemically treating the formed particles in order to achieve a high dispersion of noble metal on the catalyst.
U.S. Pat. No. 4,683,214 discloses a process for preparing a noble metal-containing zeolite catalyst of high noble metal dispersion. The process comprises crystallizing a zeolite from a forming mixture which contains an organic template, treating the zeolite by calcining or chemical oxidation to remove the template from the zeolite, mulling the zeolite with an inorganic oxide binder and a noble metal-containing solution and thereafter extruding the blended mixture.
Platinum-containing zeolite catalysts have become important bifunctional catalysts for processes such as catalytic dewaxing and reforming. Platinum may be incorporated into the zeolite matrix by impregnation or by ion exchange. Ion exchange is generally preferred, as it is believed to yield a more shape-selective catalyst.